Making Sense of the Senses... Part One

A ‘sense’ is defined as any system which consists of a group of sensory cell types which respond to specific stimuli, convert this to nerve signals which are carried to a particular part of the brain where the signals are received, interpreted and turned into meaningful sensations
1,2.

A common understanding of our senses is that humans see, touch, smell, taste and hear. Modern neuroscience is challenging this and suggesting there might be up to 33 senses. This month we explore the basic and internal senses plus some controversial senses! A key insight is the sensory receptors are often not working in isolation. For example, touch can have elements associated with pain, temperature or pressure. Sight can have elements associated with colour and contrast vision as well as interpretation of the nature of the object or where it is in space3.

Flavour is a rich example of sensory interaction: what we call the “taste” of food largely comes from smell rather than taste buds. A loss of smell will greatly affect one’s eating experience. Flavour experiences are also affected by colour, spatial arrangements and even sounds. These effects demonstrate that multisensory interactions are the rule rather than the exception3.

The senses are reviewed below plus controversy and more controversy!

Part 2 next month will explain what happens to the senses as we age and Part 3 will follow on with how designing for the senses becomes so important.

Sight (opthalmoception): How we see using two distinct types of receptors - one for color (cones) and one for brightness (rods). Visual perception, depth, recognition and interpretations all occur later as cognitive functions (i.e. post sensory).
Smell (olfacoception): How we detect scent – interpreting odour molecules which excite receptors more or less strongly.
Taste (gustaoception): How we taste substances - sweet, salty, sour, bitter, and umami (umami receptors detect the amino acid glutamate which is a taste generally found in meat and some artificial flavouring). This is different to flavour which depends on odour, texture and temperature as well as taste.
Hearing (audioception): Our hearing and auditory sense such as detecting vibrations. Distance, recognition and interpretations all occur later as cognitive functions (i.e. post sensory).
Touch (tactioception): Our tactile sense which is mainly from receptors in the skin. This is distinct from pressure, temperature, pain, and even itch sensors.

Internal Senses4,5

Proprioception: This kinesthetic sense gives you the ability to tell where your body parts are relative to other body parts, how we are positioned in space and to plan our movements. Examples include scratching an itch on your foot but never once looking at your foot to see where your hand is relative to your foot or typing without looking at the keyboard.
Equilibrioception: How we sense body movement in terms of acceleration and directional changes and attain/maintain balance. This sense also allows for perceiving gravity. Balance is the result of visual, vestibular and proprioceptive systems working together.
Thermoception: How we sense temperature – the ability to determine hot and cold.
Nociception: How we feel pain. This was once thought to simply be the result of overloading other senses, such as “touch”, but this has been found not to be the case and instead it is its own unique sensory system. There are three distinct types of pain receptors: cutaneous (skin), somatic (bones and joints), and visceral (body organs).

Additional Senses4,5
Tactility or pressure: How we respond to variations in pressure ie firm, brush, sustained.
Itch: This is a distinct sensor system from other touch-related senses.
Tension Sensors: These are found in such places as your muscles and allow the brain the ability to monitor muscle tension.
Stretch Reception: Senses of gag reflex, gas distention, excretion, control of respiration etc via stimulus from muscles, joints and skins.
Chemoreception: Senses of hunger, thirst, vomiting and suffocation through stimulus via blood or brain.
Cutaneous reception: Sense of skin vasodilation (flushed skin)

Controversial5:
Magnetoception: How we sense direction. This is the ability to detect magnetic fields, which is principally useful in providing a sense of direction when detecting the Earth’s magnetic field. Unlike most birds, humans do not have a strong magentoception, however, experiments have shown it is present.
Chronoception: How we sense the passing of time. This one is debated as no singular mechanism has been found that allows people to perceive time. However, experimental data has conclusively shown humans have a startling accurate sense of time, particularly when younger.
More Controversial4:
Sixth sense: Sense of intuition (gut feeling)
Premonition: Subconscious sense of future events (usually danger)
Telepathy: Auditory perception of a person’s (near or far) thoughts
Precognition: Visual perception of future events
Clairvoyance: Visual perception of invisible objects or events